The present invention relates to oral compositions which contain fluoride in suitable concentrations. It has surprisingly been found that diluted hydrofluoric acid applied on dental hard tissues at pH 2.5-4.5 reduce their solubility to up to 90%, when these are subsequently exposed to erosive acids. The oral compositions of the present invention are thus formulated to reduce solubility of teeth and prevent or stop, development of dental erosions.
Dental erosions represent loss of dental hard tissues (enamel, dentine and cementum) presumably due to excessive consumption of acidic beverages, juices or fruits. In some cases concerning subjects with eating disturbances, strong acid from the stomach may reach the oral cavity and cause severe dental erosions. Food and beverages may contain or weak inorganic acids which may provide a pH as low as 3 or less, on the tooth surfaces, whereas the strong acid from the stomach may yield a pH at 1.5 or below.
Teeth are very strong and resistant against mechanical wear, but dissolves and lose their integrity at pH levels below pH 5.5. Dental erosions are related to dental caries, which also is caused by organic acids. However, in the case of caries the organic acids are formed in small amounts by bacteria located on the tooth surfaces (bacterial plaque) during metabolism of dietary carbohydrates, in particular sucrose.
The carious lesions formed are in areas which are usually covered with dental plaque (i.e. along the gingival margin, aproximally and in occlusal fissures. The caries process is progressing slowly and is caused by small amounts of acids. pH levels below 5.5 are known to cause cavities over time, and in dental cementum the “critical pH” is as high as pH 6. This is due to the chemical properties of cementum, which contains more carbonate than enamel, and thus has a higher solubility. The caries process produce cavities (i.e. localized loss of hard tissue underneath dental plaque, whereas dental erosions involve loss of hard dental tissue over whole surfaces. Dental erosions are caused by acids originating from the diet (or from the stomach) and involves most frequently the lingual and buccal aspects of the incisors, and the occlusal surfaces of molars, mainly the mandibular molars.
Dental caries was previously a major public health problem in the industrialized world. The use of fluoride prophylaxis, mainly in the form of fluorinated toothpaste, has improved the situation markedly, and dental caries is now mainly found in high risk groups, which constitute about 10% of the population in the industrialized world. Dental erosions are on the other side, found in large numbers of teenagers, that consume high amounts of acidic beverages. It appears that some individuals have higher resistance against these challenges than others, and all individuals with high consumption of acidic beverages do not contract dental erosions. Fluoride toothpaste and other conventional methods designed to stop dental caries, are not effective against dental erosions. The mechanism of the inhibition of caries by fluoride, is now well understood. It was originally thought that fluoride worked solely by reducing the solubility of enamel at the pH related to dental caries (pH 5.5-4.5). However, it is now realized that fluoride works mainly by re-mineralization. If fluoride ions are available in the plaque during a pH challenge in plaque, the calcium and phosphate released from the plaque become supersaturated with respect to fluorapatite (with contribution by the fluoride ions in plaque), and this solid phase is re-deposited on the tooth surface, thus eliminating the loss of mineral. However, this re-mineralization can only occur at pH above 4.5 and conventional fluoride methods are thus not effective concerning dental erosions which originate at pH levels below 4.5, as discussed above.